Testing materials for resilience and stiffness

ABSTRACT

RESILIENCE AND STIFFNESS OF A FABRIC SPECIMEN ARE DETERMINED FROM MEASUREMENTS OF THE TENSILE LOAD THAT INDUCES A MINIMUM OSCILLATION IN A FABRIC SPECIMEN AND THE TIME REQURIED FOR AN INITIAL COMPLETE OSCILLATION CYCLE AT THE TENSILE LOAD. AN APPARATUS USEFUL FOR MAKING THESE MEASUREMENTS COMPRISES MEANS FOR SUBJECTING THE SPECIMEN TO A LONGITUDINAL TENSILE LOAD, MEANS FOR HOLDING AN END OF THE SPECIMEN AND MEANS FOR APPLYING A RELEASABLE TORQUE TO ANOTHER END AROUND THE LONGITUDINAL AXIS OF ROTATION OF THE SPECIMEN WHILE THE SPECIMEN IS SUBJECTED TO THE TENSILE LOAD TO THEREBY TWIST THE SPECIMEN THROUGH AN ANGLE OF ROTATION, AND MEANS FOR MEASURING THE TIME PERIOD AND OSCILLATION CYCLES UPON RELEASE OF THE SPECIMEN FROM THE APPLIED TORQUE. MEANS ARE PROVIDED FOR MECHANICALLY MEASURING THE APPLIED TENSILE LOAD AND THE APPLIED RELEASABLE TORQUE. MEANS ARE ALSO PROVIDED FOR ELECTRICALLY SENSING AND MECHANICALLY RECORDING THE OSCILLATION PERIOD OF THE SPECIMEN FROM APPLICATION OF TORQUE TO DAMPING AFTER RELEASE.

n NQV- I L'.E'.KELKL EY ET-AL 3,613.0,1

, TESTING MATERIALS FOR RESILIENCE AND STII'NESS 'RAYMOND a.; ALExANoERaf;

EDWARD'. M.` sloMA 'Y i ATTORNEY' Nov. 16, 1971 Filed June 5. 1970 L. E.KELLEY ETAL 3,620,071

TESTING MATERIALS FOR RESILIENCE AND STIFFNESS 2 Shoots-Sheet 2 zPREolsIou lb c Powen SUPPLY ANGULAR zERolNG DISPLACEMIENT-T.Willi/[IIIA- clRculT TRANsoucER l2 VARIABLE faz sPAN REcoRoER FIG 3 FIG.v 4.

INVENTORS LOUIS E. KELLEY RAYMOND B. ALEXANDER 8| EDWARD M. SIOMAATTORNEY United States Patent O 3,620,071 TESTING MATERIALS FORRESILIENCE AND STIFFNESS Louis E. Kelley, Wyncote, Raymond B. Alexander,Philadelphia, and Edward M. Sioma, Levittown, Pa., assignors to Rohm andHaas Company, Philadelphia, Pa.

Filed June 5, 1970, Ser. No. 43,874 Int. Cl. G01n 3/26 U.S. Cl. 73-99 5Claims ABSTRACT F THE DISCLOSURE Resilience and stiffness of a fabricspecimen are determined from measurements 0f the tensile load thatinduces a minimum oscillation in a fabric specimen and the time requiredfor an initial complete oscillation cycle at the tensile load. Anapparatus useful for making these measurements comprises means forsubjecting the specimen to a longitudinal tensile load, means forholding an end of the specimen and means for applying a releasabletorque to another end around the longitudinal axis of rotation of thespecimen while the specimen is subjected to the tensile load to therebytwist the specimen through an angle of rotation, and means for measuringthe time period and oscillation cycles upon release of the specimen fromthe applied torque. Means are provided for mechanically measuring theapplied tensile load and the applied releasable torque. Means are alsoprovided for electrically sensing and mechanically recording theoscillation periods of the specimen from application of torque todamping after release.

This invention relates to the testing of fabric specimens. Inparticular, it relates to an apparatus for measuring the tensile loadthat induces a minimum oscillation in a fa-bric specimen upon release ofthe specimen from twisting around a longitudinal axis. The apparatusalso measures the time period required for an initial completeoscillation cycle. The invention also relates to a method ofsimultaneously determining resilience and stiffness of a fabricspecimen.

The present invention particularly relates to the testing of non-wovenfibers which are fibrous of filamentous products having a carded fiberstructure or comprising fibrous mats in which the fibers or filamentsare distributed haphazardly or in random array including array of fibersin a carded web wherein partial orientation is frequently present aswell as other arrays in which the fibers are in a completely ha'phazarddistributional relationship.

These bonded non-woven fibrous products are useful in the production ofarticles of either flat or three-dimensional shape, including insulatingmaterial and the like.

Particularly the bonded fibrous products are used as textile products inarticles of dress, for example, as interliners for the collars and cuffsof shirts, especially the relatively open-weave type used for summerwear.

Bonded non-woven fabrics suitable for interlinings and the like requirea combination of rubbery resilience and solvent-resistance properties.Non-woven fabrics are generally evaluated by experts for resilience,bounce, softness, stiffness, harshness, etc. by wadding a piece ofmaterial in the hand and releasing it. The hand senses the resistance tocrushing and feels the spring-back of the fabric when the pressure isreleased. The emphasis of the test is on the instantaneous reaction ofthe fabric. This process, however, is tedious and is influenced bysubjective evaluation and is sometimes of questionable value. There hasbeen a long-felt need in the art for quantitative procedures andapparatus for establishing ICC absolute standards to replace thesesometimes variable and, at best, approximate testing means. Developmentof such procedures and apparatus has not been immediately forthcomingbecause of the difficulty of developing dynamic mechanical testsnecessary to determining the properties of non-woven fabrics thatcontribute to resilience particularly snap-back from crushing.

The 'present invention fulfills this long-felt need and provides amethod and apparatus for simultaneously determining resilience andstiffness which have been found to be respectively relatable to thetensile load that induces a minimum oscillation in a fabric specimen andthe time period required for an initial oscillation cycle at this load.The present invention, although preferably applicable to the testing ofnon-woven fibers, is applicable to the testing of any flexible materialin which stiffness and resilience are characteristic properties. Theapparatus of the present invention, described in its broadest terms,comprises means for subjecting a fabric specimen to a longitudinaltensile load, means for holding an end of the specimen and means forapplying a releasable torque to another end around the longitudinal axisof rotation of the specimen while the specimen is subjected to thetensile load to thereby twist the speciment through an angle ofrotation, and means for measuring time period and oscillation cyclesupon release of the specimen from the applied torque.

The method of the present invention, described in its broadest terms,comprises subjecting a fabric specimen to a longitudinal tensile load,twisting the specimen through an angle of rotation by applying areleasable torque load around the longitudinal axis of the specimenwhile the specimen is subjected to the tensile load, releasing thespecimen from the applied torque to cause the specimen to oscillatearound its axis of rotation and measuring the tensile load required andtime for an initial complete oscillation. For purposes of thisspecification, an initial complete oscillation, is the first completeoscillation after release of torque where ffl/A2 is between 2.5 and 3.5,preferably equal to or less than 2.7, A1 and A2 being respectively theamplitude of a first and second oscillation peak. This will be describedin more detail infra. The ranges and values for ffl/A2 above, arepreferred values. The invention is useful for testing thecharacteristics of fiber specimens at any constant A1/A2 relationship solong as the A1/A2 ratio is such that meaningful values are obtainable.

FIG. 1 of the drawings is a front elevation view of a preferredembodiment of the present invention showing the testing device andspecimen to be tested.

FIG. 2 is a plan View of FIG. 1.

FIG. 3 is a functional diagram of the electronics associated with theapparatus of FIGS. 1 and 2.

FIG. 4 shows curves A and B which represent the oscillations of a fabricspecimen around its longitudinal axis upon release of an applied torque.

Referring to FIGS. 1 and 2, the apparatus is set on a base 1 whichsupports a platform 2. A tension sensing device 3 is mounted on theplatform 2. The sample being tested, designated S, is a strip of fabricwhich is held by means of specimen clamps 4 and 5. Specimen clamp 4 isattached to tension sensing device 3 so that the fabric sample can besubjected to a determined amount of tension which is recorded by thedevice 3. Once the strip has been subjected to tension, the end of thestrip is clamped between lock jaw clamp 6 and stand 7 both of which aremounted on the lock jaw clamp base 8. While the strip is being mountedbetween the specimen clamps 4 and 5, it is supported on a raised sampleleveler platform which is mounted at hinge 10. The platform 9 issupported at a horizontal position by leg 11 while the strip is mounted(not shown). After the strip has been clamped in place by jaw clamp 6,leg 11 is lowered and the platform 9 falls away from the specimen,pivoting around hinge to a rest position as shown.

Clamp 5 is fixed to rotary shaft 12 and collar 13. Collar 13 isgraduated for the purpose of indicating the degree of rotation aroundthe axis of rotary shaft 12. The collar 13 is also grooved forengagement with finger 14 which is pivotally mounted at 15 on housing16. Housing 16 additionally encompasses an angular displacementtransducer (not shown) which is connected to rotary shaft 12 -forpurposes as will be described later. Clamp 5, rotary shaft 12 and collar13 are slidably mounted via housing 16 on screw rail 17. The housing 16can be longitudinally moved along rail 17 by turning knob 18 to therebyincrease or decrease the tension on a specimen held between clamps 4 and5.

In operation, a sample S is placed between clamps 4 and 5. The sample issupported and leveled by raised sample platform 9. A tension is placedon the sample by moving housing 16 and hence clamp 5, longitudinallyalong rail 17 away from clamp 4. Lock jaw clamp 6 is then applied to thesample to hold it in a fixed position against stand 7, and leg 11 isremoved to lower leveler platform 9. Shaft 12 and collar 13 are thenrotated, thereby twisting sample S to a particular angle. Finger 14 isengaged with a notch on collar 13 to hold the sample at the chosen angleof rotation. The finger 13 is then disengaged so that the sample androtary shaft 12 are allowed to rotate freely. This free rotationdevelops a voltage in the connected angular displacement transducerportional to the arc of the oscillations of the shaft.

FIG. 3 is a functional diagram of the electronics associated with theapparatus of FIGS. 1 and 2. In FIG. 3, a regulated, D.C. power supply 19provides a stable voltage source for a precision electrical bridgenetwork composed of two precision potentiometers and their respectivesliders or movable taps and indicated 20 and 21. One potentiometer 20serves as a zero control to position a recorder stylus (in block 22) at0 rotation. The other potentiometer 21 serves as an angular displacementtransducer, the voltage outlet of which is directly proportional to theangle of rotation of the sample specimen S connected to thepotentiometer 21 by means of clamp 5 and rotary shaft 12 (shown in FIGS.1 and 2). The output of the electrical bridge net-work is measured by avariable span recorder 22 and is recorded by a stylus on a recordingtape (not shown).

In principle the test specimen is the oscillating member of a torsionpendulum where one end of the specimen is rigidly clamped while theother end is attached to a moment of inertia member (rotary shaft 12 andcollar 13) which is free to oscillate to twist and untwist the specimen.As discussed in Mechanical Properties of Polymers, Nielsen (1962) at pp.141 to 143 the time required for one complete oscillation of twisting isthe period P. Damping gradually converts the mechanical energy of thesystem into heat so that the amplitudes (indicated A in FIG. 4) of theoscillations decrease with time. Shear modulus may be calculated fromthe periods of the oscillations. The shorter the period the greater themodulus. The damping, expressed as the natural logarithmic decrement A,is calculated from the rate at which the amplitude of the oscillationsdecreases. If the damping is high (the natural logarithmic decrement isgreater than 1.0) the oscillations die out rapidly and measurementscannot be made. If the natural logarithmic decrement is equal to or lessthan 1.0, shear modulus for rectangular shapes is calculated as follows:

(i) :mamie-4M C-width of specimen in inches D-thickness of specimen ininches I-polar moment of inertia of the oscillating system P-period ofoscillation in seconds u shape factor depending on ratio of width tothickness of specimen It is preferable, in the present invention, to usetest specimens of the same size within a comparative test group. Withstandard specimen sizes then:

so that l/P2 indicates the relative shear modulus of the specimen andhence the stiffness. [t should be noted here though that the presentinvention is not limited to testing of specimens of the same size butcan be applied to the testing of specimens of varying size with sizevariations corrected to comparable shear modulus values by utilizationof the above Formula 1.

Damping, the logarithmic decrement A, is calculated from the logarithm(to the base e) of the ratio of two successive oscillations:

where A1 and A2 are the amplitudes of successive oscillations of thesample as illustrated in FIG. 4. If damping is too high, A l.0 then thefabric specimen is placed under a tensile load to thereby decrease thedamping to obtain oscillations which can be measured. A plot of l/P2against applied tensile loads can then be extrapolated to zero t0provided the correct period for determining shear modulus. Thus theminimum tensile load on a strip of fabric which will cause it tooscillate after twisting is the load at which oscillation A1 divided byoscillation A2 equals 2.7 (the natural logarithm of 2.7 is 1.0). Rubberymaterials which recover from deformation instantaneously, oscillateunder little or no tensile load. It has been found in the presentinvention that the fabrics rated as rubbery by experts are those whichwill oscillate from a rotation of with 25 grams or less tensile load ona fabric strip 2 inches long by 0.5 inch wide. When tensile load isplotted against 1/ P2 at A=l.0, relative positions for fabric specimenswith respect to stiffness and resilience are obtained.

In the following examples, a sample 2 inches long by 0.5 inch Wide isplaced between the clamp of the testing device of FIGS. 1 and 2. Thefabric sample is supported and leveled by a sample platform and lockedinto a fixed position by a lock jaw clamp. The sample platform is thenremoved. A tension load -is placed on the sample and the shaft of theapparatus of FIGS. l and 2 is rotated to 135 thereby twisting thesample. The shaft is released and the shaft and sample are allowed torotate freely. The instantaneous amplitude of the oscillations ofrotations are measured by means of a recording tape. This tape is markedlengthwise in l mm. units, accented at 5 mm. with heavy accent at l0 mm.When the sample is at the flat, untwisted position, a Stylus indicatesthe center line of the tape. Twisting the sample through an angle of 135brings the stylus to the top line of the tape. The tape travels at aconstant speed of 50 mm./second. Since a log `decrement of 1.0 indicateshigh damping all measurements are taken on first oscillations. The valueP (period in seconds) is taken as one complete cycle from the releasepoint through the first low point and back to the top peak. Thelongitudinal distance for the first oscillation is measured in mm. andconverted to seconds. The amplitudes of the first two peaks below thecenter line are measured and the logarithmic decrement A is calculatedfrom the logarithm (to the base e) of the ratio of the amplitudes of thetwo successive oscillations. As given in Formula 3 A=ln .4l/A2 where A1is the amplitude of the first oscillation and A2 is the amplitude of thesecond oscillation.

Even the most resilient fabrics have relatively high damping (ascompared to a steel spring) and some tensile load is generally necessaryto obtain two complete osare given to the panel. A minimum of four teststrips are cillations that have sucient amplitude to be measured. cutfrom different pads. The critical amplitudes selected are those giving alog de- The samples are prepared by padding a cross laid noncrementA=1.0 or lower. The tensile load and shear woven polyester web weighing1 oz. per square yard with modulus l/P2 at these critical amplitudes arecharacter- 5 a 10% solids solution of the formulated polymer emulisticof a fabric specimen. Since tensile load is inversely sions indicated inTable 1. The padded webs are supported related to resilience and shearmodulus is stiffness, the two on glass marquisette, partially driedunder infrared, airqualities (stiffness and resilience) arequantitatively dedried overnight, cured for 5 minutes at 150 C.,calentermined and related among fabrics. dered at normal roll pressure,and conditioned for a mini- In comparing different materials forrelative stiffness l mum of 16 hours at 65% R.H., 70 F.

TABLE i Fabric specimen Binder composition Additive 2...' Copolymer of86 parts ethyl acrylate, 10 parts acrylonitrile and 4 parts of a None.

molar mixture of acrylamide and methylolacrylamide. 3 Copolymerff 60parts butadiene, 37 parts acrylonitrile and 3 parts meth- 5% of amelamine formaldehyde resin emulsion.

acry ic aci 4 Copolymer of 96 parts butyl acrylatc and 4 parts of a 1 to1 molar mixture of Do.

methylacrylamide and methylol methacrylamide. 5 96 paits butylacliylate, 3 5 parts N -methylol-4-pentenlguanamine, and 0.5 1% of amelamine formaldehyde resin emulsion.

paf ClY 1C acl 6 Copolymer of 96 parts butyl acrylate 5 partsN-methylol-4-pentenoguana- 5% of a polyvinyl chloride resin emulsion.

mine, and 0.5 part acrylic acid. f 7 copolymer 0196 parts butylacrylate, 4 parts of a 1:1 molar mixture of meth- 10% of a polyvinylchloride resin emulsion.

ylacrylamide and methylol methacrylamidc. 8..--.. Ethyl acrylate polymer5% of a polyvinyl chloride resin emulsion and 5% of a 50% solidsemulsion of 96.0 parts butyl acrylate, 3.5 parts N-methylol-4-pentenoguanamine and 5 parts acrylic acid.

9 do 2.5% of a polyvinyl chloride resin emulsion and 2.5% of a 50%solids emulsion of 06.0 parts butyl acrylate, 3.5 parts N-methy1ol-4-pentenoguanamine and 0.5 part acrylic acid.

and resilience, the samples are tested at different tensile In thepanelists determinations, each expert is asked to loads, increased indetermined increments until the tensile rate the fabrics for resilienceas fast, medium and loa-d is sufficient to cause the sample to oscillatein arcs in slow and to rate the hand as soft, firm or stiff which A1/A2is equal to or less than 2.7 or A is equal to Each panelist is advisedthat specimen 3 is to be conor less than 1. This tensile load ischaracteristic of the sidered firm with f-ast recovery. Specimen 3 isconsample and readings at this load are used to calculate sidered areference material and al1 other fabrics are the stiffness andresilience. rated against its standard.

EXAMPLE 1 35 Results of both the panel evaluations and testings of thefabrics by the -apparatus and process of the present 111 this example,the test Sample 1S a 0-5 by 2.0 Inch invention (as detailed in thespecification above and in rectangular strip of an interlining used forshape recovery Example 1) are given in T3131@ 2, The tensile loads arein Clothes and made from a non-WOVeIl Polyester fabric determined in 5gram increments below 25 and in 25 gram bonded together by I'CSlIlS 0fbutadiene-acrylollltflle for' 40 increments above and are those lowestloads mulated with triazine formaldehyde. give an A1/A22-7,

After clamping the piece into the testing device, an initial load of 5grams is applied and the piece is twisted TABLE 2 through an angle of135. The test specimen is then al- Resilience stiffness lowed to rotatefreely from the 1n1t1al torque of applied 45 Tensiamplitude of 135. Thecurve shown in FIG. 4, A,w repload resenting the oscillation of thesample around its'iongi- Specimen (grams) Panel l/P2 Panel tudinal axisupon release of the applied torque is ob- I t n 200 Slow Firm to stiff.tained. It 1s seen that a load of 5 grams 1s not enough to 5 give twoosicllations for this particular sample. 18 sgftto firm (softer than 3).

29 Stiffer than 3.

16 Softer than 3.

17 Soft to firm (softer than 3).

An increased load of 25 grams is applied and the sample is twistedthrough an angle of 135. The applied torque is released and the sampleis allowed to rotate freely and the curve shown in FIG. 4, B isobtained. Prom this curve, it is seen that a tensile load of 25 grams-is sufficient to give a value A1A/f2: 1.78 the natural log of which is0.576 which is less than 1. The period from FIG. 4, B, is

These examples illustrate the correlation between resilience andstiffness as determined lby the process and 13mm apparatus of thepresent invention and with previously P :m used subjective testingmethods. Generally the following or 0h26 Second and MP2: 15.0. 60correlatlons shown 1n Table 3 are indicated.

The resilience of this sample is determined to be TABLE 3 FAST by apanel of experts and the hand to be border- Resilience line between softand firm. Thus the determination of the Tensile load, decrement ofoscillation to be less than 2.0 with a 25 grams Resmee gram tensileload, icorrelates this tensile load with a fast 1-30 Fastreeovery.resilience and the l/Pe value of 15.0 is correlated with a lgo NfediumfeC0Ve1Y- hand between soft and firm. S 0W recovery' EXAMPLES 2 To 9 T ll d Stness In the following examples, measurements are made on grllse oal/P2 Stlfness the fabrics by the procedure of Example .1, and thesemeas- 1-15 Soft. urements are correlated with evaluation of the samefab- 15-30 M? 'umrics by a panel of four experts. Whenever possible inthese examples, the strips of fabric used as test specimens in the 25 4glium testing device are cut from the same pieces of fabric that Thevalues indicated in Table 3 illustrate the usefulness of the process andapparatus of the present invention for determining resilience andstiffness of fabric specimens. The process and apparatus of the presentinvention are particularly useful for determining relative resilienceand stiffness for a series of fabric specimens.

What is claimed is:

1. Ari 'apparatus for measuring the tensile load that induces a minimumoscillation in a fabric specimen and the time required for an initialcomplete oscillation cycle comprising means for subjecting the fabricspecimen to a longitudinal tensile load, and means for measuring saidload applied to the specimen, means for holding an end of the specimenand means for applying a releasable torque to another end around thelongitudinal axis of rotation of the specimen while the specimen issubjected to the tensile load to thereby twist the specimen through anangle of rotation, and means for measuring time period and oscillationcycles upon release of the specimen from the applied torque.

2. The apparatus of claim 1 additionally comprising means for recordingand representing the measured time period and oscillation cycles.

3. A method of simultaneously determining resilience and stiffness of afabric specimen comprising subjecting the specimen to a longitudinaltensile load, twisting the specimen through an angle of rotation byapplying a releasable torque load around the longitudinal axis of thespecimen While the specimen is subjected to the tensile load, releasingthe specimen from the applied torque to cause the specimen to oscillatearound its axis of rotation, and measuring the tensile load required andthe time for an initial complete oscillation.

4. The process of claim 3 in which an initial oscillation is thatoscillation at which Al/Az is between 2.5 and 3.5 where A1 and A2 arerespectively the 'amplitudes of successive complete oscillations of thespecimen.

5. The process of claim 3 in which the initial oscillation is thatoscillation at which A1/A2 is equal to or less than 2.7 at a maximumtensile load.

References Cited UNITED STATES PATENTS 2,593,389 4/1952 Nielsen 73-993,313,148 4/1967 Dautreppe et al. 73-99 JERRY W. MYRACLE, PrimaryExaminer U.S. Cl. X.R. 73-159

